Apparatus for producing powders by atomization of liquid carriers



I Sept. 2, 1958 J E NYROP- 2,850,085

APPARATUS FOR PRODUCING POWDERS BY ATOMIZATION OF LIQUID CARRIERS FiledDec. 27, 1950 2 Sheets-Sheet 1 'INVENTOR. JOHA N E. NY ROP Sept. 2, 1958J. E. NYROP 2,850,085

APPARATUS FOR PRODUCING POWDERS BY ATOMIZATION OF LIQUID CARRIERS FiledDec. 27, 1950 2 Sheets-Sheet 2 Fig.2

INVENTOR. Te. 1V YK- Unite States Patent APPARATUS FOR PRODUCING POWDERSBY I ATOMIZATION OF LIQUID CARRIERS Johan Ernst Nyrop, Hellernp, nearCopenhagen, Denmark, assignor to Niro Corporation, New York, N. Y.

Appiication December 27, 1950, Serial No. 202,940 Claims priority,application Denmark December 29, 1949 2 Claims. c1. 1s'9 4 The inventionrelates to a apparatus for producing powders by atomization of liquidcarriers.

The main object of the invention is an improved method for obtainingpowders of very little air content in a simple and cheap manner.

In many cases it will be desirable to get powders with as little aircontent as possible. By way of example should be mentioned that indifferent places certain maximum contents of air are prescribed forpackings with dried milk. For the removal of air it is common in suchcases to evacuate the packing, which has generally the form of a tin,before the closing of the latter. The free quantity of air present abovethe powder and between the particles of the powder can in this Way bequickly and easily removed, but the air incorporated in the individualparticles will diffuse very slowly so that a removal of said air will bean exceedingly lengthy affair. The air thus incorporated in theparticles plays a very important part, however, and therefore it is ofimportance to achieve a simple and quick method for its removal.

Also in many other powders, e. g. easily oxidizable powders, the aircontent in the individual particles can be regarded as detrimental, andthe purpose of the present invention is to indicate a generallyapplicable solution of said problem. The invention is based on thediscovery that an improved practical solution to this problem isobtained by producing the atomized liquid in such a manner that thepowder resulting from the drying of the atomized liquid has as little anair content as possible in preference to removing the air contentafterwards.

According to the invention powders with little air content are producedby reducing the air content of the liquid by centrifugation before theatomization, and by I preventing the absorption of air to the liquid onits way from the place ofcentrifugation to the place of finalatomization.

It proves that by this method a powder can be obtained with aconsiderably lower air content than was the case by the usual methodsfor the production of powders, and this result is presumably due to thefact that the liquid particles resulting from the atomization aresubstantially not inclined to absorb air in the drying chamber so thatthe air content of the liquid at the moment of atomization are decisiveof the air contents of the powder produced.

By the method indicated a further very important advantage is attained,viz. a high specific gravity of the powder so as to make it far lessvoluminous than powders produced by the methods hitherto used beingafterwards freed from part of their air content. This is due to the factthat an evacuation of the powder does not influence the size of theindividual powder particles. The reduced voluminousity is of specialimportance with regard to the freight costs for shipments, especiallyfor long-distance shipments.

In atomization by means of a rotating atomizer, it

is an object of the invention to utilize the centrifugal force derivedfrom the rotation of the atomizer for the removal of the air from theliquid.

The invention also concerns different apparatus for carrying out themethod indicated.

A further object of the invention is a device for producing powders witha reduced air content by atomization, said device being provided withmeans for centrifugation of the liquid before the atomization takesplace.

In some embodiments of such device the centrifugation takes place in acentrifuge means inserted in the path of the liquid between the inlet ofthe device and the atomizer.

In other embodiments especially to be realized in connection withdevices of the kind having a rotating atomizer with a vane wheel, inwhich the vanes are constituted by channels in the plate shaped wheel,the channels have a form of curvature by which a centrifugal force isexerted on the liquid on its way through a channel in such a way that aseparation of air from the liquid takes place.

Other and further objects and advantages of the invention will appearfrom the following description re ferring 'to the accompanying drawingsin which the invention will be illustrated as embodied in some diiferenttypes of apparatus.

Fig. 1 shows a partly sectional view of an atomization drying device ofknown type in which a device according to the invention is mounted.

Fig. 2 shows diagrammatically part of a device according to theinvention, partly an axial section.

Fig. 3 shows in side elevation part of another embodiment of the deviceaccording to the invention, and

Fig. 4 shows a horizontal projection of a detail of the embodiment shownin Fig. 3.

In Fig. 1 30 represents a drying chamber of a well known kind. On thetop part 31 of said chamber 30 a driving means 32, such as anelectro-motor is mounted with its shaft 1 penetrating into the dryingchamber 30. On the shaft 1 is an atomizer 33 mounted inside the chamber30. A tubular means 34 serves for supplying liquid to the atomizer 33and another tubular means 35 serves for supplying a drying medium, suchas hot air, into the chamber 30.

The structure as hitherto described is commonly known and used forthe-production of dried powders and need no further description and thespecific shape of it should mean no limitation of the invention as anyarbitrary drying device comprising a drying chamber in which a liquid isto be atomized may be mounted with a device according to the invention.

The device according to the invention is now to be described in furtherdetail by way of example with reference to Figs. 2-4.

In the embodiment diagrammatically shown in Fig. 2 a wheel-shaped plate2 is mounted on the rotating shaft 1, said plate 2 being at itscircumference provided with an upwardly-directed flange 3. On thisflange a ring-shaped plate 4 is secured which in the case shown isshaped as a vane wheel, being at its upper side provided with recesses 5which extend from the interior of the vane wheel to its outercircumference and form its vanes. On top of the plate 4 a cover 6 ismounted which closes the recesses 5 upwardly so that they form channelswhich are open only at the inner and outer circumference of the vanewheel 4, and the walls, facing the direction of rotation, of thechannels form the vanes of the vane wheel. From the parts 2, 3, and 4has thus been formed a ring-shaped, inwardly open space 7 and, as willappear from the figure, said space is divided into two chambers 8 and 9by means of a ringshaped disc 10 which terminates some distance from theflange 3 and at the inner circumference merges into a substantiallycylindrical part 11 which extends up into the ring-shaped clearancebetween the boss 12 of the plate 2 and the plate 4 and is in fixedconnection with the cover 6.

All the parts hitherto mentioned thus rotate with the shaft.

The liquid to be atomized is supplied through one or more pipes 13leading to one or more apertures 14 and one or more pipes 15 beingmounted below said aperture or apertures, resp. and leading down intothe clearance between the cylindrical part 11 and the boss 12.

In the section shown in Fig. 2 only one of the elements 13, 14, and 15resp. is shown, but in case of several such elements it should beunderstood that they are arranged in the same manner but in differentradial sections through the device.

By the action of the centrifugal force the liquid is flung out into thespace 7 and gets a mainly vertical surface substantially at the level ofthe internal circumference of the plate 4. From there the liquid flowsup to the vanes formed by the recesses 5 and is fiung out along thesurfaces of these vanes due to the action of the centrifugal force andfinally the liquid leaves the extreme edges of the vanes in an atomizedstate.

On account of the accumulation of liquid occurring in the spaces 7, 8,and 9 the liquid flows comparatively slowly through these spaces, anddue to the centrifugal force the air content in the liquid is influencedby a buoyancy directed inwards towards the axis, and this buoyancy willcause a considerable quantity of the air to move inwards towards theaxis in the chamber 8 against the direction of the fiow of liquid sothat the liquid present in the chamber 9 and going outwards to the vaneshas considerably less air content than the liquid supplied to thechamber 8.

Above the cover 6 a stationary screen 16 is mounted for preventing airfrom being sucked in by the rotation of the vane wheel. The quantity ofair released in the chamber 8 can escape through the clearance betweenthe cover 6 and the screen 16.

By using an atomizer with a vane wheel of the type shown in the figure,but without the air separator 8-11 indicated and under ordinaryoperation conditions, generally a powder with an air content of about 24cm. per 100 g. is obtained. Under the same conditions and with the samevane wheel but by the application of the air separator shown in thefigure is obtained a very substantial reduction of the air content, viz.by way of example a reduction of the air content down to 8 cm. air per100 g. powder.

Even if in the embodiment shown the vane wheel is in direct connectionwith the members causing the air separation, this is no condition forcarrying out the invention in practice, the essential feature being thatthe liquid poor in air given off from the chamber 9 is led to anatomizer of some kind or other in such a way that a renewed mixing ofthe liquid with air is substantially avoided.

Renewed absorption of air by the liquid is substantially avoided. It isnot necessary that the liquid be atomized immediately after the air hasbeen separated therefrom, the only essential condition being thatrenewed absorption be avoided before atomization.

Thus, the centrifuge means shown need not necessarily be directlyconnected with the atomizer wheel as shown. However, the particularcombination shown in the drawings and described herein is moreinexpensive to manufacture than separate elements having connectingmeans therebetween would be.

Figs. 3 and 4 show diagrammatically a centrifugation wheel for anotherembodiment of the apparatus according to the invention. This wheelcomprises a circular disc 20 and a corresponding cover plate 27connected 4. to each other by means of bolts and nuts 28 and mounted onthe shaft 1 by means of a boss 29 secured to the wheel by the same boltsand nuts 28. As shown in Fig. 4 the disc 20 is provided with a circularaperture 21. In this disc channels 23 of substantially uniform breadthhave been milled down or produced in some other way, which channelsextend from the internal periphery of the disc to its externalperiphery. 24 and 25 are holes for the bolts 28 for securing the coverplate 27 to the disc 20 and by means of said cover plate the channels 23get closed in cross section and are in communication with thesurroundings only through the inner and outer months.

The wheel is intended for rotating in the direction of the arrow asshown, and as appears from the figure the mouths of the channels 23 inthe outer periphery of the wheel are displaced in the direction ofrotation in relation to the corresponding admission openings in theinner periphery of the wheel. This is due to the fact that the channelsextend along curved lines which in the case shown have the form ofinvolutes of a circle, but need not be bound to this form.

When liquid is supplied to the wheel at the inner periphery, the walls26 of the channels, which walls lie on the side of the channels facingthe direction of motion, will act as vanes and make the liquid rotate.The centrifugal force produced thereby will cause the liquid to beforced out through the channels along said walls 26 in the form of athin film. Due to the curvature of the channels the centrifugalacceleration has a component directed at right angles to the tangent ofthe channel. According to a known physical law an acceleration field isequivalent to an opposite directed gravity field. Further when air issuspended in liquid and the liquid is subjected to a gravity field abuoyancy will act on the air. Accordingly this buoyancy is of theopposite direction as the centrifugal acceleration and so the aircontent will travel relative to the liquid in the direction of rotationat right angles to the tangent of the channel in the point in thequestion which means that the air will travel out from the liquid acrossthe channel. Both liquid and air will generally be forced out throughthe channels due to the centrifugal force but due to the said componentof the same the liquid will substantially travel along one wall in thechannel and the air along the other one. At the end of the channel, thecentrifugal force will carry the particles of liquid radially outwardly,and the same centrifugal force will prevent the absorption of air by theparticles for perhaps a short distance radially outwardly of theperiphery of the atomizer Wheel. Atomization therefore takes placebefore the liquid can absorb air.

It should be added that in a known vane wheel of an atomizer having aradial channel, the air content of the liquid passing through thechannels is also subjected to a buoyancy. This is, however, directedalong the channel i. e. in the direction of movement of the liquid withthe result that the relative movement between air and liquid may beregarded as a phase-shift since the path of the air particles in acertain portion of the liquid leaving the channel is different from thepath of the air particles contained in the same portion of liquid whensupplied to the channels, but the quantity of the air content issubstantially the same.

The best effect is obtained when the channels are curved in the form ofa spiralor evolute-curve which reckoned from its starting point andoutwards lies in increasing distance in the direction of motion of thewheel from the radius through the inner mouth of the channel.

An extremely effective separation is obtained when the angle between thetangent to the channel curve and the radius through the point oftangency for all points of a channel is substantially constant and. aslarge as possible.

It will be understood that the angle cannot become which shouldtheoretically give the best possible utilization of the centrifugalforce. This would, however, necessitate that each channel should wind asa spiral with an infinite number of terms which cannot be obtained inpractice, and at the same time the driving force becomes very small. inpractice it is therefore necessary that the angle be a certain amountless than 90. The closer the angle can approach to 90 the better is thecentrifugal force utilized for the air separation and therefore theangle is as close to 90 as permitted by the construction in combinationwith regard to obtaining the necessary driving force for the liquid.

The wheel shown may in itself serve as an atomizer wheel and can thusdirectly substitute for the atomizer wheel of a corresponding size in anordinary rotating atomizer.

The atomization brought about by the wheel may, however, also beregarded as a preliminary stage of the complete atomization so that theliquid flung out from the wheel may through difierent further sprayingmembers he led to the final atomizer.

'It is, however, also possible to use the wheel shown in Figs. 3 and 4in connection with the apparatus shown in Fig. 1 so that the channels inthe vane wheel 5 are shaped like the channels 23 shown in Fig. 4.

The channels need not necessarily be shaped in the manner shown in Fig.4, since other forms may be used where a component of the centrifugalacceleration is obtained at right angles to the tangent to the channelcurve thereby obtain the inventive effect.

It is also pointed out that with a wheel of the type shown in Fig. 2 andwith radial channels, under normal operation conditions a powder isobtained with an air content of about 24 cm. per 100 g., whereas inaccordance with the invention, there is obtained a reduction of the aircontent to about 8 cm. air per 100 g. powder.

The figures given for the two embodiments of the apparatus are to beunderstood as illustrative since a still greater reduction of the aircontent may be obtained in accordance with various obvious modificationsof the invention, the reduction being substantially dependent on thedesign of the channels and the velocity of rotation =used.

On the basis of the above detailed explanation of the parts being moreessential for the invention it is thought that all details not shown ordescribed or only mentioned in short in the foregoing will be apparentto those skilled in the art.

It should, however, be understood that the above description of a fewembodiments shown on the drawing should have no limiting effect on theinvention as any possible changes in size, proportions, shape anddetails may be made and any other possible means than those shown may beused in practising the new method, all within the scope of the appendedclaims.

I claim:

'1. In a device for production of powders by atomization of a liquid,having a drying chamber, a disc-shaped vane wheel suspended in saidchamber, a shaft secured to said wheel, means for rotating the shaft,said wheel having a central opening from which the vanes of said wheelextend to the periphery of said wheel, each of said vanes being shapedas a wall and defining a channel of substantially uniform breadth withone of the other vanes,

the channels extending from the central opening to the,

direction of motion of said Wheel as defined by said' means for rotatingsaid shaft, the magnitude of the curvature being such that thecentrifugal force derived from the rotation of said wheel has acomponent at right angles to the channel and the angle between thetangent to the curvature of said channels and the radius through thepoint of tangency being only a little less than for all points of achannel.

2. Centrifugation means for separating air from liquid comprising adisc-shaped wheel having an opening concentrically in the middle ofthewheel, means for rotating said wheel, walls in said wheel definingchannels extending from said opening to the outer periphery ofthe-wheel, said channels being curved so as to deviate from the radiusof said wheel in the direction of rotation of the wheel, the anglebetween the tangent to the curvature of said channels and the radiusthrough the point of tangency being only a little less than 90 for allpoints of a channel and means for supply of liquid to the said channelsthrough said opening in the wheel.

References Cited in the file of this patent UNITED STATES PATENTS2,003,575 Bowen June 4, 1935 2,233,855 Suss Apr. 4, 1941 2,238,364 HallApr. 15, 1941 2,289,191 Hall July 7, 1942 2,290,470; Hall July 21, 19422,294,221 Bowen Aug 25, 1942 2,312,474 Peebles Mar. 2, 1943 2,357,050McCrum Aug. 29, 1944 2,450,599 Kloda Oct. 5, 1948 2,473,035 Meade June14, 1949. 2,515,665 Pieper July 18, 1950 2,587,083 Andermatt Feb. 26,1952 2,602,002 Schutt July 1, 1952 FOREIGN PATENTS I 4,798 AustraliaApr. 5, 192 65,538 Denmark Aug. 11, 1947 162,678 Great Britain May 12,1921 269,774 Great Britain Apr. 28, 1927 6 68 Netherlands May 15, 1948

